The Source of Plasma Dihydrotestosterone in Man

The source of plasma dihydrotestosterone (DHT) (17beta-hydroxy-5alpha-androstan-3-one) in humans has been investigated by infusing two potential peripheral precursors, testosterone (T) and androstenedione (A). Metabolic clearance rates (MCR), conversion ratios (CR), transfer constants (rho), and blood production rates (P(B)) were calculated. Plasma testosterone and dihydrotestosterone were measured by competitive binding techniques. The MCR(DHT) was 652 +/-35 (SD) liters/day in five males and 314 +/-63 (SD) liters/day in four adult females. In each individual, the MCR(DHT) was significantly lower than MCR(T) as predicted by testosterone-binding protein affinity studies. The P(B) (DHT) was 302 +/-65 (SD) mug/day in males and 56 +/-26 mug/day in females. Testosterone and androstenedione are precursors (prehormones) for plasma dihydrotestosterone. The conversion ratio CR(BB) (T-DHT), calculated as the ratio of counts per minute per liter of plasma of product to precursor after infusion of labeled precursor, was 5.6 +/-0.6 (SD)% (six subjects) in the male and 3.5 +/-0.4 (SD)% (four subjects) in the female. CR(BB) (A-DHT) after androstenedione infusion to three female subjects averaged 9.2%. No dihydrotestosterone back conversion was detected (< 0.2%). The transfer constants were [rho]BB(T-DHT), 3.9 +/-1.0% (male) and 1.7 +/-0.6% (female), and [rho]BB(A-DHT) average was 13.3% in three female subjects. Using either plasma testosterone and dihydrotestosterone values from our subjects and mean androstenedione values as reported in the literature, approximate contributions can be calculated. Testosterone conversion accounts for at least 70% of plasma DHT in the male, but less than 20% in the normal female. Androstenedione appears to be a major prehormone of plasma dihydrotestosterone accounting for at least two-thirds plasma dihydrotestosterone by peripheral conversion in adult females. In three normal women undergoing tubal ligation, there was an unimpressive gradient between ovarian vein and peripheral plasma dihydrotestosterone. It is suggested that dihydrotestosterone in the blood does not arise from direct secretion but may reflect events occurring in peripheral androgen target tissues.     

The metabolic clearance rate and origin of plasma dihydrotestosterone in man and its conversion to the 5α-androstanediols

Dihydrotestosterone metabolism was studied with a constant infusion technique in three men, three women, five hirsute women, and four estrogen-treated hirsute women. The mean dihydrotestosterone metabolic clearance rate was higher in men (336 liters/24 hr per m(2) [range, 239-448]) than in women (153 liters/24 hr per m(2) [range, 108-184]). The metabolic clearance rates in hirsute patients were intermediate between those men and women and were decreased by estrogen treatment. These observations demonstrate similarities in the metabolic rates of testosterone and dihydrotestosterone.The conversion of plasma testosterone and androstenedione to dihydrotestosterone was studied in men and hirsute women. Approximately 4 and 2% of plasma testosterone and androstenedione, respectively, were converted to plasma dihydrotestosterone in both groups. From these observations it was determined that a major fraction of plasma dihydrotestosterone was derived from these plasma precursors rather than from glandular secretion.Both 5alpha-androstan-3alpha,17beta-diol (3alpha-diol) and 5alpha-androstan-3beta,17beta-diol (3beta-diol) were identified in plasma during dihydrotestosterone and testosterone infusions. The conversion ratio of dihydrotestosterone to 3alpha-diol (C(BB) (DHT-3alpha)) was greater than the conversion ratio to the 3beta-isomer (C(BB) (DTH-3beta)) in all the patients studied. Both C(BB) (DHT-3alpha) and C(BB) (DHT-3beta) were higher in men (mean values of 0.151 [range, 0.110-0.222] and 0..031 [range, 0.022-0.042]) than in women (means of 0.044 [range, 0.037-0.048] and 0.012 [range 0.010-0.013]). A smaller fraction of testosterone was converted to 3alpha-diol and 3beta-diol.     

Metabolic clearance rate and blood production rate of testosterone and dihydrotestosterone in normal subjects, during pregnancy, and in hyperthyroidism

The metabolic clearance rate (MCR) and blood production rate (BP) of testosterone (T) and dihydrotestosterone (DHT), the conversion of plasma testosterone to plasma dihydrotestosterone, and the renal clearance of androstenedione, testosterone, and dihydrotestosterone have been studied in man. In eight normal men, the MCR(T) (516+/-108 [SD] liters/m(2)/day) was significantly greater than the MCR(DHT) (391+/-71 [SD] liters/m(2)/day). In seven females, the MCR(T) (304+/-53 [SD] liters/m(2)/day) was also greater than the MCR(DHT) (209+/-45 [SD] liters/m(2)/day) and both values were less than their respective values in men (P < 0.001). In men the conversion of testosterone into dihydrotestosterone at 2.8+/-0.3% (SD) was greater than that found in females, 1.56+/-0.5% (SD) (P < 0.001). In five pregnant females the MCR(T) (192+/-36 [SD] liters/m(2)/day), the MCR(DHT) (89+/-30 [SD] liters/m(2)/day) and the conversion of testosterone into dihydrotestosterone (0.72+/-0.15%) (SD) were significantly less than the values found in nonpregnant women. In five females with hyperthyroidism, the MCR for testosterone and dihydrotestosterone were similar to those observed in pregnant females, but the conversion of testosterone into dihydrotestosterone (2.78+/-1.7%) (SD) was greater, and similar to that found in men. In men the production of dihydrotestosterone was 0.39+/-0.1 (SD) mg/day, 50% being derived from the transformation of plasma testosterone. In women the production of DHT was 0.05+/-0.028 (SD) mg/day, only 10% coming from testosterone. During pregnancy, the production of testosterone and dihydrotestosterone are similar to that in normal women. In three patients with testicular feminization syndrome (an adult with hyperthyroidism and two children) these two MCRs were greatly reduced compared to the normal females, but the conversion of testosterone into dihydrotestosterone was in the limits of normal male rangeIn the normal subjects the renal clearance of androstenedione was greater than that of testosterone and dihydrotestosterone. Less than 20% of the dihydrotestosterone and less than 10% of the androstenedione in the urine is derived from the plasma dihydrotestosterone and androstenedione.     

Testosterone and Androstenedione Blood Production Rates in Normal Women and Women with Idiopathic Hirsutism or Polycystic Ovaries

The average plasma testosterone concentration of women with either hirsutism or polycystic ovaries and hirsutism was higher (p < 0.01) than that of normal women although the ranges overlapped. Testosterone blood production rates averaged 830 +/- 120 SE and 1,180 +/- 310 SE mug per day in the two groups of hirsute women and 230 +/- 33 SE mug per day in normal women. The ranges did not overlap.The testosterone metabolic clearance rates of hirsute women (1,090 +/- 140 SE L per day) and of men (1,240 +/- 136 SE L per day) were significantly higher than those of normal women (590 +/- 44 SE L per day). These differences persisted when the metabolic clearance rates were corrected for surface area. We suggest that testosterone metabolic clearance rates vary directly with some function of testosterone production.The mean plasma androstenedione levels (2.8 +/- 0.35 SE and 2.8 +/- 0.30 SE mug per L) and production rates (6,060 +/- 450 SE and 7,360 +/- 345 SE mug per day) of the women with hirsutism or polycystic ovaries, respectively, were significantly higher than those of normal women (1.5 +/- 0.22 SE mug per L; 3,300 +/- 830 SE mug per day). The androstenedione metabolic clearance rates were the same in each group. Plasma androstenedione was the precursor of 49% of plasma testosterone in normal women and of 26% of plasma testosterone in hirsute women. Thus, 74% of the plasma testosterone in these subjects must have been either secreted or derived from a precursor that did not enter the plasma androstenedione pool.     

Metabolism of prostaglandins A1 and E1 in man.

To investigate the in vivo whole blood metabolic clearance rates and sites of metabolism of prostaglandins A1 and E1 in man, constant infusions of the tritiated compounds were administered to normal subjects and to patients undergoing cardiac catheterization. The whole blood metabolic clearance rate of [3H]prostaglandin A1 in eight men was 5,003 +/- 864 liters/day (SD) or 2,546 +/- 513 liters/day per m2 (SD). Nonradioactive prostaglandin A1 was similarly infused in two subjects, and the metabolic clearance rates were determined, utilizing a specific radioimmunoassay. The clearance rates with this method correlated closely with those determined by the isotope infusions. Extraction studies of prostaglandin A1 showed that pulmonary, splanchnic, renal, and extremity perfusions resulted in 8.1 +/- 4.1, 56.1 +/- 10.1, 50.3 +/- 3.4, and 34.4 +/- 5.9% (SEM) removal, respectively. With [3H]=prostaglandin E1, the whole blood metabolic clearance rate was determined from the pulmonary artery concentration in three patients and averaged 4,832 +/- 1,518 liters/day (SD) or 2,686 +/- 654 liters/day per m2 (SD). Pulmonary extraction was 67.8 +/- 6.8% (SEM) and extremity removal averaged 6.6 +/- 4.9% (SEM). These results indicate that A prostaglandins are metabolized by several organs, such as the liver and kidney, and possibly by intravascular pathways as well. In man, the E prostaglandins are primarily metabolized by the lung, but extraction is not complete and approximately one-third may escape lung metabolism. Thus, these findings suggest that both E and A prostaglandins in the venous circulation may reach the systemic circulation in man.     

A decreased metabolic clearance rate of aldosterone in benign essential hypertension

Aldosterone secretion rate, metabolic clearance rate, and/or plasma concentration were determined in 16 patients with benign, uncomplicated essential hypertension and compared with those of control subjects. The mean metabolic clearance rate of aldosterone in 10 patients was significantly (P < 0.001) lower (mean 867 liters of plasma/day per m(2) +/-270 SD) than in a group of 7 healthy subjects (mean 1480 liters/day per m(2) +/-265 SD). Secretion rates in 13 patients (including the 10 already mentioned) tended to be low (83 +/-43 vs. 109 +/-54 mug/day) and plasma concentrations tended to be high (13.6 +/-4.6 vs. 7.5 +/-4.8 ng/100 ml), but neither of these differences was statistically significant.The lower metabolic clearance rate could account for elevated plasma concentrations of aldosterone even when the secretion rate is normal or low. Measurement of secretion rate or urinary excretion only is therefore insufficient to establish the presence and/or mode of evolution of hyperaldosteronism. Failure of the aldosterone secretion to adapt fully to a decreased aldosterone metabolic clearance rate (MCR) could explain the state of relative hyperaldosteronism in patients with benign essential hypertension, even when the secretion rate and the urinary excretion rate are in the normal range.     

An assessment of daily production and significance of thyroidal secretion of 3, 3', 5'-triiodothyronine (reverse T3) in man.

While 3, 3', 5'-triiodothyronine (reverse T3, rT3) has been detected both in human serum and in thyroglobulin, no quantitative assessment of its metabolic clearance rate (MCR), production rate (PR), or secretion by the thyroid is yet available. This study examines this information in euthyroid subjects and evaluates it in light of similar information about two other iodothyronines in the thyroid: 3, 5, 3'-triiodothyronine (T3) and thyroxine (T4). Thus, it was noted that rT3 is cleared from human serum at a much faster rate than are T3 and T4; the mean (+/-SE) MCR of rT3 was 76.7+/-5.4 liters/day in 10 subjects, whereas MCR-T3 and MCR-T4 in 8 of them were 26.0+/-2.2 liters/day and 1.02+/-0.06 liters/day, respectively. Therefore, even though the mean serum concentration of rT3, 48+/-2.8 ng/100 ml, was much lower than that (128+/-6.7 ng/100 ml) of T3, the mean PR-rT3 (36.5+/-2.8 mug/day) and the mean PR-T3 (33.5+/-3.7 mug/day) were similar; in comparison, the mean serum concentration and PR of T4 were 8.6+/-0.5 mug/100 ml and 87.0+/-3.9 mug/day, respecitvely. These data and those on the relative proportion of rT3, T3, and T4 in 10 thyroid glands were used to assess the significance of the contribution of thyroidal secretion to PR-rT3 and PR-T3. It was estimated that whereas thyroidal secretion may account for about 23.8% of serum T3 (or PR-T3), it may account for only about 2.5% of serum rT3 (or PR-rT3). Since peripheral metabolism of T4 is the only known source of rT3 and T3 other than the thyroidal secretion, it could be calculated that as much as 73.0 mug or 84% of daily PR-T4 may normally be metabolized by monodeiodination either to T3 or to rT3. MCR and PR of various iodothyronines were also examined in five cases with hepatic cirrhosis, where, as documented previously, serum rT3 may be elevated while serum T3 is diminished. The mean MCR-rT3 in these cases (41.0 liters/day) was clearly (P is less than 0.005) less than that (76.7 liters/day) in normal subjects. This was the case at a time when the mean MCR-T3 (26.7 liters/day) and the mean MCR-T4 (1.19 liters/day) did not differ from those (vide supra) in normal subjects. Distinct from changes in MCRs, the mean PR-rT3 (33.0 mug/day) was similar to, and the mean PR-T3 (10.1 mug/day) and the mean PR-T4 (66.4 mug/day) were much less than, the corresponding value in normal subjects. Furthermore, while the ratio of PR-rT3 and PR-T4 (rT3/T4) in individual patients was either supranormal or normal, the ratio of PR-T3 and PR-T4 (T3/T4) was clearly subnormal. The various data suggest that: (a) just as in the case of T3, the thyroid gland is a relatively minor source of rT3; peripheral metabolism of T4 is apparently its major source; (b) the bulk of T4 metabolized daily is monodeiodinated to T3 or to rT3; (c) monodeiodination may be an obligatory step in metabolism of T4; (d) monodeiodination of T4 to rT3 is maintained normal or is increased in hepatic cirrhosis at a time when monodeiodination of T4 to T3 is decreased.     

Metabolic clearance and plasma disappearance rates of human pancreatic tumor growth hormone releasing factor in man.

The metabolic clearance rate (MCR) and plasma disappearance rate (t1/2) of human pancreatic tumor growth hormone releasing factor [hpGRF(1-40)] was determined in normal adult male subjects by single injection and constant infusion techniques. Single injections of 1, 3.3, and 10 micrograms/kg hpGRF(1-40) were administered intravenously, plasma immunoreactive (IR) GRF levels were measured during the subsequent 180 min, and biexponential curve analysis was performed. Graded, dose-constant infusions of hpGRF(1-40) at rates of 1, 3.3, 10, and 33 ng/kg per min were administered and the MCR was calculated from measurement of steady state plasma IR-GRF levels at each infusion rate. The postinfusion disappearance rate was determined by linear regression analysis of plasma IR-GRF levels during the 120-min period after cessation of the infusion. The calculated MCR during the single injection study was 194 +/- 17.5 liters/m2 per d and was not significantly different from the calculated value during the constant infusion study (202 +/- 16 liters/m2 per d). The disappearance rate during the single injection study was subdivided into two linear phases: an initial equilibration phase (7.6 +/- 1.2 min) and a subsequent elimination phase (51.8 +/- 5.4 min). The latter was similar to the linear disappearance rate observed (41.3 +/- 3.0 min) after cessation of the constant infusion. The chromatographic and biologic characteristics of plasma IR-GRF, 30 min after injection, were similar to those of synthetic hpGRF(1-40). The results have been discussed in relation to the MCR of other hypothalamic hormones and have been used to extrapolate secretion rates of GRF in patients with ectopic GRF production.     

Pharmacokinetic Studies of Tobramycin and Gentamicin

Broth dilution susceptibility tests of 100 isolates of Pseudomonas aeruginosa and 101 isolates of Staphylococcus aureus against tobramycin (formerly nebramycin factor 6) and gentamicin showed that tobramycin was more effective against P. aeruginosa and less effective against S. aureus. The minimal inhibitory concentration of tobramycin against the Pseudomonas sp. isolates that required 5 mug of gentamicin per ml for inhibition ranged from 0.63 to 0.31 mug/ml. Peak concentrations in the blood of 10 healthy adults after intramuscular injection of 80 and 40 mg of tobramycin averaged 3.7 +/- 0.62 and 2.4 +/- 0.27 mug/ml, and declined to 0.56 +/- 0.05 and 0.26 +/- 0.02 mug/ml, respectively, after 6 h. The urine recovery averaged 60%. The half-life was 1.6 h. During continuous intravenous infusion of tobramycin and gentamicin (infusion rate 6.6 mg per h), blood levels at steady state were 0.94 +/- 0.10 and 1.04 +/- 0.06 mug/ml, respectively. For both antibiotics, the calculated distribution volume ranged from 15 to 17 liters. The renal clearance to tobramycin averaged 76% and that of gentamicin averaged 85% of the total clearance, indicating that the drugs are primarily eliminated by the kidneys. The present results suggest that tobramycin may be more successful in the treatment of Pseudomonas infections than gentamicin at the same dosage (80 mg intramuscularly three to four times daily).     

Metabolic clearance rate of radioiodinated human growth hormone in man

The nature of the disappearance of radioiodinated human growth hormone (HGH) from plasma has been reexamined. The metabolic clearance rate (MCR) was determined both from single injection and constant infusion studies. After single injection of highly purified radioiodinated HGH, the disappearance curve remained multiexponential during the period of study (4 hr). The shape of the curve was independent of the growth hormone preparation used. Similar disappearance curves were obtained with unlabeled HGH.MCR values calculated from constant infusion studies were 203 +/-7.8 liters/day per m(2) and values derived from single injection studies agreed closely with this.The multiexponential nature of the disappearance curve does not permit meaningful calculation of volume of distribution or half-time of disappearance.     

Sex-specific action of insulin to acutely increase the metabolic clearance rate of dehydroepiandrosterone in humans.

To test the hypothesis that insulin acutely enhances the metabolic clearance rate (MCR) of dehydroepiandrosterone in humans, the effect of a short-term insulin infusion on the MCR of dehydroepiandrosterone was assessed in 10 men and 7 women. After an overnight fast, dehydroepiandrosterone was infused at 3.47 mumol/h for 6.5 h. At 240 min, a hyperinsulinemic-euglycemic clamp was begun by infusing insulin at 21.5 pmol/kg per min for 2.5 h. MCR of dehydroepiandrosterone was calculated at baseline (210-240 min) and during the insulin infusion (360-390 min). A control study was conducted at least 1 wk later, in which 0.45% saline was substituted for the hyperinsulinemic-euglycemic clamp. During the insulin clamp study, serum insulin rose from 34 +/- 2 to 1084 +/- 136 pmol/liter (P = 0.0001) in men and from 40 +/- 5 to 1357 +/- 175 pmol/liter (P = 0.0003) in women, while serum glucose remained constant in both groups. MCR of dehydroepiandrosterone rose in men during the insulin infusion from 2443 +/- 409 to 3599 +/- 500 liters/24 h (P = 0.003), but did not change during the control saline infusion. In contrast, MCR of dehydroepiandrosterone in women did not change in the insulin clamp study during insulin infusion (2526 +/- 495 liters/24 h at baseline vs. 2442 +/- 491 liters/24 h during insulin infusion; P = 0.78). These findings suggest that insulin acutely increases the MCR of dehydroepiandrosterone in men but not in women.     

3 alpha, 17 beta-androstanediol glucuronide in plasma. A marker of androgen action in idiopathic hirsutism.

Biologically active androgens and peripheral androgen metabolites in plasma were measured in 25 women with idiopathic hirsutism (IH). Plasma testosterone was not significantly elevated. Free testosterone however was increased although the elevation was not impressive (10.9 +/- 6.6 SD vs. 3.3 +/- 1.5 ng/dl) and one-fourth of the cases had normal unbound testosterone. Dihydrotestosterone (DHT) values were elevated (23.5 +/- 14 vs. 12.5 +/- 3.59) but again over half of the values were within the normal range. In our series of mild to moderate cases, 3 alpha-diol was not at all discriminatory. However, plasma 3 alpha-diol glucuronide was markedly increased (604 +/- 376 vs. 40 +/- 10 ng/dl), and elevated in all but one mild case. Previous studies document that DHT is the important androgen in skin and formation of DHT and 3 alpha-diol is markedly increased in vitro in IH. Since 3 alpha-diol glucuronide is derived largely from extrasplanchnic events, beta-glucuronidase is present in skin, and androgen stimulates formation of the enzyme in extrasplanchnic tissue, we conclude that 3 alpha-diol glucuronide is a marker of peripheral androgen action and markedly elevated in IH.     

Metabolic clearance rate of arginine vasopressin in severe chronic renal failure.

1. The metabolic clearance rate of arginine vasopressin was determined using a constant infusion technique in normal subjects and patients with chronic renal failure immediately before commencing dialysis. Endogenous arginine vasopressin was suppressed in all subjects before the infusion with a water load. 2. Plasma arginine vasopressin concentrations were determined using a sensitive and specific radioimmunoassay after Florisil extraction. The detection limit of the assay was 0.3 pmol/l, and intra- and inter-assay coefficients of variation at 2 pmol/l were 9.7% and 15.3%, respectively. 3. In normal subjects, the metabolic clearance rate was determined at two infusion rates producing steady-state concentrations of arginine vasopressin of 1.3 and 4.4 pmol/l. In the patients with renal failure, a single infusion rate was used, producing a steady-state concentration of 1.5 pmol/l. 4. At comparable plasma arginine vasopressin concentrations, metabolic clearance rate was significantly reduced in patients with renal failure (normal 1168 +/- 235 ml/min versus renal failure 584 +/- 169 ml/min; means +/- SD; P < 0.001). 5. Free water clearance was significantly reduced in normal subjects during the arginine vasopressin infusion from 8.19 +/- 2.61 to -1.41 +/- 0.51 ml/min (P < 0.001), but was unchanged in the patients with renal failure after attaining comparable plasma arginine vasopressin concentrations. 6. In normal subjects there was a small but significant fall in metabolic clearance rate at the higher steady-state arginine vasopressin concentration (1168 +/- 235 ml/min at 1.3 pmol/l versus 1059 +/- 269 ml/min at 4.4 pmol/l; P = 0.016).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics and dynamics of (+/-)-verapamil in lean and obese Zucker rats

To evaluate the mechanism of obesity-induced changes in pharmacokinetics and pharmacodynamics of verapamil observed in humans, single-dose and steady-state kinetic/dynamic studies in obese Zucker rats were done. Seven lean and five obese Zucker rats received a single dose of verapamil (2 mg/kg) and plasma samples were obtained for verapamil concentrations over the following 7 hr. Terminal elimination half-life was significantly prolonged in obese animals compared to lean (mean +/- S.D., 2.68 +/- 0.87 hr obese vs. 1.39 +/- 0.35 hr lean; P less than .01) due to the significantly increased total volume of distribution observed in the obese animals (1.62 +/- 0.28 liters obese vs. 0.83 +/- 0.14 liters lean; P less than .001). There was no significant difference in the total clearance (0.45 +/- 0.16 liters/hr obese vs. 0.43 +/- 0.10 liters/hr lean; NS) between lean and obese animals. A physiological explanation for the increased volume of distribution was evaluated by determining actual distribution of verapamil into tissue during steady-state infusion. Six lean and six obese animals received a loading infusion of verapamil (25 micrograms/min) for 1.2 hr in lean and 1.6 hr in obese rats followed by a constant infusion of 5 micrograms/min for the next 2.5 to 3 hr. Steady-state clearance was similar between groups (0.349 +/- 0.095 liters/hr obese vs. 0.244 +/- 0.066 liters/hr lean; NS). Plasma verapamil concentration at the termination of steady-state infusion was similar between lean and obese rats (0.91 +/- 0.24 microgram/ml obese vs. 1.26 +/- 0.33 microgram/ml lean).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dehydroepiandrosterone sulfate: kinetics of metabolism in normal young men and women

The constant infusion technique was used to study the kinetics of dehydroepiandrosterone sulfate (DHEAS) metabolism in normal young men and women. The metabolic clearance rates (MCR) (means +/- SEM) for normal young men and women were 15.2 +/- 1.7 1/24 h (8.2 +/- 0.7 1/m2/24 h) and 11.8 +/- 0.8 1/24 h (7.3 +/- 0.4 1/m2/24 h) respectively. Coupled with the plasma levels of 5.07 +/- 1.95 and 4.02 +/- 0.57 mumole/L the resulting blood production rates were 76.7 +/- 25.7 and 48.0 +/- 9.4 mumole/24 h for men and women respectively. The conversion ratios for the conversion of DHEAS to dehydroepiandrosterone (DHEA) were 0.006 for men and 0.004 for women. Because of the high metabolic clearance rates for DHEA relative to those for DHEAS and the high production rates of DHEAS most of the DHEA produced per day can arise from DHEAS.     

Production rates and metabolic clearance rates of human follicle—stimulating hormone in premenopausal and postmenopausal women

The production rates (PR) and the metabolic clearance rates (MCR) of human follicle-stimulating hormone (HFSH) were determined in six pre- and five postmenopausal women. Human FSH (PER-780) labeled with (131)I to specific activities of 50-150 muc/mug was used as a tracer. Both double antibody and trichloroacetic acid (TCA) precipitation techniques were used to determine HFSH-(131)I levels in infusate and plasma. In four of the subjects MCRs measured by both constant infusion and single injection techniques were the same. By constant infusion, plasma HFSH-(131)I levels reached equilibrium between 4-5 hr.MCRs in six premenopausal women were 14.2+/-1.1 (mean +/-SE) ml/min. MCRs in five postmenopausal women were 12.6 +/-1.1 ml/min. Simultaneous HFSH and human luteinizing hormone (HLH) MCRs were determined in a single patient using HFSH-(125)I and HLH-(131)I as tracers by both constant infusion and single injection methods. These studies showed that the MCR of HFSH was 10.8-11.1 ml/min, and the MCR of HLH was 18.5-19.4 ml/min. From these data and previous MCR and PR studies of HLH from this laboratory, it appears that the MCR of HFSH is about one-half that of HLH.Endogenous HFSH and HLH levels were measured by radioimmunoassay. The PRs of HFSH, calculated by the product of endogenous level and MCR, were 146 +/-27mU/min in the premenopausal women and 2141 +/-264 mM/min in the postmenopausal women. 24-hr PRs, based on these results, compared with reports of 24-hr urinary excretions of biologically active HFSH indicate that 3-5% of production is found in urine in biologically active form. After our single injections of HFSH-(131)I, 8-29% was recovered in urine over 24 hr.     

Dihydrotestosterone in prostatic hypertrophy: I. The formation and content of dihydrotestosterone in the hypertrophic prostate of man

To explore the relation between androgens and prostatic hypertrophy in man, the concentrations of testosterone, dihydrotestosterone, and androstenedione and the rate of conversion of testosterone to dihydrotestosterone have been measured in normal and hypertrophic prostate tissue. First, a double isotope derivative technique was adapted for the measurement of tissue androgen content in 15 normal and 10 hypertrophic prostates. Although there was no significant difference in the content of androstenedione and testosterone between the two types of tissue, the content of dihydrotestosterone was significantly greater in the hypertrophic tissue (0.60 +/-0.10 mug/100 g) than in the normal glands (0.13 +/-0.05 mug/100 g). Second, a regional study was performed in three normal prostates and four glands with early hypertrophy, and it was demonstrated that the dihydrotestosterone content was two and three fold greater in the periurethral area where prostatic hypertrophy usually commences than in the outer regions of the gland. Finally, the rate of conversion of testosterone to dihydrotestosterone has been measured under standardized conditions in tissue slices from 4 normal and 20 hypertrophic prostates. There was no significant difference in the rate of dihydrotestosterone formation between the two types of gland (6.0 +/-0.8 and 7.8 +/-0.5 mumumoles/15 mg of tissue per hr). While the mechanism by which dihydrotestosterone accumulation occurs remains unexplained, it is possible that the local accumulation of dihydrotestosterone may be involved in the pathogenesis of prostatic hypertrophy in man.     

Metabolic clearance of biologically active luteinizing hormone in man.

The plasma metabolic clearance of biologically active luteinizing hormone (bioactive LH) was studied using the rat interstitial cell testosterone (RICT) bioassay in six hypogonadotropic men after single bolus injection of highly purified human LH and during continuous steady-state infusions of three graded doses of LH. The LH bolus disappearance curves provided estimates of metabolic clearance rates (MCR) of 24.1 +/- 4.7 (+/- SD) ml/min for bioactive LH vs. 56.2 +/- 12 ml/min for immunoactive LH in the same men (P = 0.03). A lower MCR of bioactive LH compared with immunoactive LH was also observed during continuous infusions of physiological doses of LH; for example, the mean steady-state MCRs for bioactive and immunoactive LH were, respectively, 26.1 +/- 3.1 and 34.2 +/- 3.2 ml/min (P = 0.02). Moreover, the stepped-dose infusion regimens permitted us to demonstrate that increasing doses of pure human LH resulted in progressive and parallel decreases in the apparent MCRs of both bioactive and immunoactive LH. Based on the respective steady-state MCRs calculated at physiological plasma concentrations of immunoactive and bioactive LH, we estimate a mean endogenous production rate for bioactive hormone of 1,937 IU/24 h, and for immunoactive LH of 589 IU/24 h in normal men. These results indicate that previous estimates of LH production rates from immunoassay data alone markedly underestimate the quantity of biologically active hormone secreted in man.     

Piperacillin pharmacokinetics in subjects with chronic renal failure

The pharmacokinetic parameters of piperacillin sodium were studied in eight volunteer subjects with chronic renal failure. Subjects were given a single 30-min intravenous infusion of 70 mg/kg (lean body weight) on their off-dialysis day. Blood was drawn from the contralateral arm at 15 and 30 min and 1, 3, 6, 9, and 12 h from the start of the infusion. Kinetic parameters were determined during the elimination phase with a one-compartment open model for linear kinetics. The following pharmacokinetic parameters (mean +/- standard deviation) were determined for the eight subjects: elimination half-life = 3.33 +/- 0.99 h, elimination rate constant = 0.22 +/- 0.06 h-1, apparent volume of distribution = 0.18 +/- 0.05 liters per kg, and total body clearance = 0.041 +/- 0.019 liters per kg/h. The mean peak serum concentration was 372 +/- 125 microgram/ml, and mean trough at 12 h was 39 +/- 27 microgram/ml. A dose of 70 mg/kg (lean body weight) or a dose of 4 g appears to provide adequate serum concentrations against susceptible organisms for a 12-h interval. No adverse reactions were noted in any subject throughout the study.     

Pharmacokinetics of Isepamicin during Continuous Venovenous Hemodiafiltration

The objective of this study was to analyze the pharmacokinetics of isepamicin during continuous venovenous hemodiafiltration. Six patients received 15 mg of isepamicin per kg of body weight. The mean isepamicin concentration peak in serum was 62.88 +/- 18.20 mg/liter 0.5 h after the infusion. The elimination half-life was 7. 91 +/- 0.83 h. The mean total body clearance was 1.75 +/- 0.28 liters/h, and dialysate outlet (DO) clearance was 2.76 +/- 0.59 liters/h. The mean volume of distribution was 19.83 +/- 2.95 liters. The elimination half-life, DO clearance, and volume of distribution were almost constant. In this group of patients, the initial dosage of 15 mg/kg appeared to be adequate, but the dosage interval should be determined by monitoring residual isepamicin concentrations in plasma.